Electric motor control system



p 1940- E. A. BINNEY ET m. 2,214,605

' ELECTRIC MOTOR CONTROL SYSTEM Filed Sept. 7. 1939 WITNESSES: Q QINVENTORS l Frz'cABzbney, Harold S .Pozmd- Comer awwiw Nd H O; ugh B.Sedgfzeld 2 M B I 9 M! M ATT Patented Sept. 10, 1940 ELECTRIC MOTORCONTROL SYSTEM Eric Alton BinneyI Ilkley, and Harold SinclairPound-Comer and Hugh Brougham Sedgfield, Bradford, England, assignors toThe English Electric Company, Limited, London, England, a company ofGreat Britain Application September 7 1939, Serial No. 293,695.

. In Great Britain September 8, 1938 12 Claims.

This invention relates toelectric power equipment in which aWard-Leonard or a booster set is adapted to draw electric energy from anexternal power supply and to supply or to buck or boost .the supply to adirect current motor to accelerate the motor. The invention furthermorerelates to particular equipment of this kind including transfer switchesby means of which the load formed by the motor armature ,can betransferred wholly to the said power supply. Qertain arrangements ofthis kind are described in the specification of the copendingapplication oi C. E. Baston and E. A. Binney, Serial No. 157.855. filedAugust 6, i937.

An object of the present invention is to provide for' the completeautomatic control of traction motors, both on power and regeneration.

Another object of this invention is to provide a motor control system inwhich no changes are made to the power connections in transferring frompower to regenerative braking.

A further object of the invention is to provide a motor control systemwhich will maintain substantially constant current over a wide range ofoperation.

Other objects will be explained fully hereinafter or will be apparent tothose skilled in the art.

The invention consists in controlling the transfer switches by meansresponsive to some electrical condition of the circuit of the workingmotor such as the potential difference between two points in thecircuit. Transference is thus dependent on the electromotive force ofthe .generator or booster or on the back electromotive force of theworking motor. In particular, where transference is effected by closureof switches between points which have first been brought tosubstantially the same potential, 'the control means respond to acondition of substanti'ally no difference in potential between the saidpoints. The transfer may be entirely automatic, under the sole controlof the said control means and the latter may also control retransferenceof the load back to the generator or booster.

The invention furthermore comprises various automatic control andprotective features for a complete equipment of the kind referred to.Such features will appear from the following description of oneparticular form of buck and boost control equipment for electrictraction motors, as shown in the accompanying drawing.

In the single figure showing one particular complete system for thecontrol of two direct current electric traction motors or two groups ofmotors on the buck and boost system and insur porating the presentinvention. the booster set comprises three machines. viz: (a) thecompound-wound machine I connected between the.

supply lead 2 and the common earth connection 3, (b) the exciter I, and(c) the booster 0, all on the common shaft 4. The machine I has a seriesfield winding is and a shunt field winding lb. The booster 6 has a shuntfield winding to in series with which is the armature of the exciter I.m

The booster armature can be connected in series with and between the twotraction motors I and lb by closure of contactor Ila. These motors haveseries field windings Ia and 1c and also field windings Id and is whichcan be connected 3 a biasing winding which is opposed by In and is shownas supplied by the battery 0 through the resistor l.

The booster set can be started by closing in sequence a series ofcontactors II and I! which connect machine I-for use as the drivingmotor-to the supply line 2. On closure by the driver of a startingswitch 29 the contactor II is closed. As the motor I accelerates, thecontactor II, connected in shunt to the armature'of machine I andresponding to the increase in motor back electromotive force withincrease of speed, is closed to connect the traction motors and thebooster to the power conductor 2.

In addition to the previously mentioned contactor its there are providedtransfer ccntactors Ila and I2b, by closure of which the traction motorsI and lb can be connected in parallel with each other across the powersupply. The operation of transfer contactors Ila and Ilb isautomatically controlled, as explained hereinafter, by the. meansforming the primary feature of the invention. Initially, and during thestarting-up of the booster set, the contactors I2. Ila and its are openand the reversing switches Ito .and lie for the exciter field winding lbare in the position shown, whereby this winding is unenergized. SwitchesIto and Ilb connect the motor field windings Id and is across the powersupply.

Movement of the'drivers controller 2! to a power position makes acircuit from the positiveterminal of an auxiliary supply-which may bethe battery 9-by way of contact IIb and 29a through the operating coilII to earth, whereupon switch Ila is operated to connect one end of theu exciter iield winding 5b to the battery I to energize this winding.Another control circuit is made through the contacts III) on thecontactor II, the contacts Ila of an automatic control relay and theoperating coil II whereupon contactor Iia closes to connect the motorsand booster in series across the power supply. The operating coils II ofthe automatic control relay are connected in series with some iorm oirectilying valve Il between a positive point on the battery I and thatcontact oi the contactor III; which is connected to the boosterarmature. Reverslble polarizing coils Ilb for the control relay areconnected to the auxiliary supply through the reversing switch II.

1 The current through the booster and motor armatures is determined bythe exciter I in the circuit of the booster ileld winding Ia. Theresistance in this circuit is so adjusted that the booster issubstantially self-exciting and the eiciter, therefore, has little workto do. The exciter always influences the booster voltage in such a wayas to tend to reduce the exciter voltage to zero, 1. e., it tends tomaintain such a traction motor current that the excitation produced bythe'neld winding Ia on the exciter substantially balances that producedby any other field windings thereon. The exciter may include a shuntfield winding Id. It is also shown as having a field winding Icconnected by switch 'IIcacross the contacts of contactor IIa. Beiore theclosure of contactor IIa the current'in fleld winding 5a is negligible.Since winding so is also unenergized, the exciter tends to maintain acondition or substantially no current in winding 5c. Thus'the boosterelectromotive force tends to keep steadily equal and opposite to theelectromotive force of the power supply. Closure oi! contactor IIashort-circuits winding 50, but winding to is immediately energized andthe electromotive force ialls until there passes through the winding Iaa current which just balances the action of winding 5b. The motors arethen automatically acmlerated at this current. The driver's controller29 may include means 28b for varying the resistance I and determiningthe motor current. As the back electromotive force of motors 1 and 1bincreases, the electromotive force of the booster decreases steadily tozero, reverses, and then increases until it is equal to the supplyvoltage. When this condition is reached, there is no appreciablepotential difference across the contacts of either or the transferswitches Ila and Ilb and they can be closed without causing disturbance.

One end of the circuit or the control relay coil II is always at a smallpositive potential with respect to earth, as determined by the batteryI. The other end is at a continuously changing potential which, whencontactor IIa first closes, is substantially that oi the supply lead 2.The valve II at first, however, prevents any appreciable current frompassing through the coil II to earth. The potential of this same pointialls as the bucking electromotive iorce of the booster decreases,continues to tail, until the booster electromotive force has reversedand is assisting the supply voltage, and becomes substantially earthpotential when the booster electromotive force is equal to the supplyvoltage. The battery can then send suillcient' current through the valveI2 and the coil II to operate the control relay and change over theswitch Ila against the biasing spring I4. Certain types or rectifyingvalue-such as the static contact type employing conducting platseparated by unidirectionally conductive layershave such considerableresistance in their conductive direction that the use of one of these asthe valve Il necessitates considerable reverse potential to operate therelay II. The application of biasing voltage by the battery I overcomesthis difllculty and allows of adjustment so that the relay will operateat any desired small diilerence 0! potential between the boosterterminal and earth.

The throwing over of contacts IIa energizes first the coil ll iorclosing the contactors Ila and Ilb immediately, and second, the coil IIior throwing over the contacts Ila-alter a time delay-tor reversing thepolarizing coil III) or the control relay. The same action of contactsIla deenergizes the coil I6 whereby, alter the closure of contactors Ilaand Ilb, the contactor IIa, opens. Three other sets of switching means,viz, IIa, IIb, IIc, IId and He, operate with the contacts IIa and may beactuated by the same coil. The motors I and lb are now connected inparallel across the power supply while the circuit from the supplythrough the booster is interrupted by contactor lid. The motor fieldcoils 1d and le are connected across the booster by the movement ofswitches II and IIa while the exciter armature connections are reversedby the switches IId and IIe. The exciter ii'eld winding Ia remains inseries with motor I while the winding be, now connected in parallel withcontactor Ila by the throwing-over of switch IIc, is short-circuited bycontactor Ila and remains unenergized'. Thus the booster, by its actionon the excitation of the traction motors, continues to influence themotors and tend to maintain a predetermined motor current.

The control relay is such that the passage of a certain minimum currentthrough the coil II in an invariable direction determined by the valveIt tends to throw over the contacts Ila in one direction or the other asdetermined by themrection of current through the polarized coilIIb. Thespring II retains the contact arm in either position until overcome bythe joint action oi an operating coil and a polarizing coil. The coil IIis now connected across the open contacts of contactor Ila, just as itwas previously across the open contacts of contactor Ila when the latterwas open and the former closed, and again the potential diflerence is insuch a sense that the valve I2 prevents the passage of any appreciablecurrent. Should the changing booster electromotive force at any timebring the potential diiterence back to the value that it had at themoment when transfer was initiated, the battery will send currentthrough the coil II in the same direction as before. The coil I") being,however, reversed by contacts II this current impulse will cause thecontacts IIa to move back to their original position, energizing coil IIto reclose contactor IIa, while deenergizing coils Il and II to opencontactors Ilb and Ila and otherwise to restore the original conditionsof series connection of motorsiand booster. Since transient conditionsfollowing transfer or retransier may cause a ilow of appreciable currentthrough the operating coil II immediately after the throwing over oi therelay and the reversal of the polarising coil III), which would lead tothe relay being thrown back again, and so on, contacts IIa act with atime-lag. Any form of time delay device, such as a dashpot, as shown, orother suitable time delay mechanism, may be used. It will bescenthatcoilll macro-contactor Ilawhan that contactor is open and socontrols its closure in accordance with theeondltion of substantiallysero potential diii'erence across it. Similarly, the coil is acrosscontactor Ila when that is open.

In order to ensure that lie. andlib close before lta opens and that "a.recioses before lid and lib open, the solenoids which operate theseswitches may be of the retarded type, as shown. If desired, the sameresult may be accomplished in a well-known manner by so interlocking theswitches lia, lib and Ila that Its cannot open until lid and lib haveclosed and lie and lib cannot open until "a has closed.

The system herein described may be used to maintain substantiallyconstant current over a wide range. If desired, an axle driven machineit may be included and used to vary the excitation of field windingsIdand 'l'e inversely as vehicle speed. A switch Ila. for switchingmachine it into the circuit of field winding lb and simul-, taneously,to compensate for the electromotive force of machine lll, varying thenumber of cells of battery 0 in circuit, may be operated under thecontrol of the driver or in automatic response to vehicle speed. Thus,for example, a relay ll connected across the armature of machine it maybe adapted to pick up at a certain predetermined voltage, i. e., at acertainpredetermined vehicle speed, and actuate switch Ila. when thetransfer contactors lid and lib close and contactor lla opens, and thebooster is merely supplying field windings Id and Is, any furtherincrease of vehicle speed, by acting on the excitation of the boosterthrough the action of the machine it on the exciter, causes theexcitation of the traction motors to decrease and vice versa.

Coasting may be brought about at any time by reducing the current in thehim field winding lb of the exciter substantially to zero whereby the Qexciter will tend to maintain zero current in the traction motorarmature circuit, either directly, when motors and booster are inseries, or indirectly by tending to so excite the motors that no motorarmature current flows when the motor Q armatures are in parallel acrossthe supply. If

coasting be introduced under the latter conditions, the control relaywill still function as described to cause retransfer in response tochanges in the booster electromotive force. Power or regenerativebraking conditions can be smoothly introduced at any time byslteringthebiasing of the exciter, the transition being undisturbed byfluctuations in supply voltage. I

Regenerative braking may be introduced at any time by moving driver'scontroller 20 to a brake position. The axle-driven machine Ill may beused to control regenerative braking in accordance with speed down tothat speed at which the above-mentioned relay drops out or alternativelythe axle-driven machine may be put out of circuit ,by the driver'scontroller during regenerative braking if the latter is to be carriedout at constant current independently of speed. The switch it when in abraking position opens the circuit of operating coil ll but closes thecircult of coil l8. Switch Ila is thus as shown while switch its israised to its uppermost position. This reverses the polarity of exciterfield winding lb. The exciter then tends to maintain a condition inwhich the current through field winding la is also reversed but kept ata predetermined value. Regenerative braking at a controlled current isthus set up. The current is determined either directly by the boosterelectromotive force whmmotorsandboosterarsinseriesorbythe action of thebooster on motor excitation when the motors are in parallel. I

If braking be introduced during parallel connection of the motors, themotors will slow down and the booster electromotive force will increaseto strengthen the motor excitation either sufficiently to maintain asubstantially constant current or, if machine Ill be in circuit, to agreater extent in accordance with the decrease in speed. .This goes onuntil the booster electromotive force reaches such a value that thecontrol relay acts to restore the series connection. Thereafter brakingcan go on until the motors are brought to a standstill, and if nochanges be made, the torque would, in fact, reverse the motors, to runthe vehicle backwards. Means responsive to speed, such as a relayconnected across machine It and dropping out when the voltage of thismachine falls below a predetermined minimum,

, may interrupt the circuit established by the controller is when thelatter is in a braking position and a veryslow speedha's been reached.The same means maycontrol other circuits for introducing mechanicalbraking.

It willbe seen that the central feature of th automatic control systemis the control relay lla operated by coils 3i. This could alternativelyallow the driver to operate the transfer contactors lia and lib whenconditions are favorable but preferably the action is, as shown,entirely automatic, whereby the control by the driver is made extremelysimple. The application of the invention to other forms of buck andboost control or to Ward-Leonard control will be readily understood fromthe foregoing.

Since numerous changes may be made in the above-described construction,and different .embodiments of the invention may be made withoutdeparting from the spirit and scope thereof, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawing shall be interpreted as illustrative and not in alimiting sense.

We claim as our invention:

1. A motor control system comprising a directcurrent motor, an externalpower supply, a booster setdisposed to draw electrical energy from theexternal power supply and to buck or boost the supply to the motor,transfer switches by means of which the load formed by the motorarmature can be transferred wholly to said power supply, control meansfor said transfer switches responsive to the electrical condition of thesaid motor, and a rectifying valve in series with an operating coil ofthe control meanswhereby the said means will respond to'a potentialdifference of only one polarity.

2. A motor control system comprising a directcurrent motor, an externalpower supply, a

booster set disposed to draw electrical energy*' from the external powersupply and to buck or boost the supply to the motor, transfer switchesby means of which the load formed by the motor armature can betransferred wholly to said power supply, control means for said transferswitches responsive to the electrical condition of the said '3. A motorcontrol system comprising an, ex-

ternal power supply, a booster set disposed to draw electrical energyfrom the external power supply, two motors with the booster armaturedisposed to be connected between them to buck or boost the supply to themotors, transfer switches disposed to connect junction points of thebooster and the motor armatures with terminals of the said power supply,and a control relay for controlling the operation of said transferswitches, said relay having an operating coil connected across thecontacts of a transfer switch.

4. A motor control system comprising an external power supply, a boosterset disposed to draw electrical energy from the external power supply,two motors with the booster armature disposed to be connected betweenthem to buck or boost the supply to the motors, transfer switchesdisposed to connect junction points of the booster and the motorarmatures with terminals of the said power supply, a switch fordisconnectingthe booster from the said supply after closure of thetransfer switches and a control relay for controlling the operation ofsaid transfer and disconnecting switches, said relay having an operatingcoil connected across the contacts of said disconnecting switch.

5. A motor control system comprising an external power supply, a boosterset disposed to draw electrical energy from the external power supply,two motors with the booster armature disposed to be connected betweenthem to buck or boost the supply to the motors, transfer switchesdisposed to connect junction points of the booster and the motorarmatures with terminals of the said power supply, a switch fordisconnecting the booster from the said supply after closure of thetransfer switches, and a con trol relay for controlling the operation ofsaid transfer and disconnecting switches, said relay having an operatingcoil connected across a transfer switch when the transfer switch is openand across the disconnecting switch when it is open.

6. A motor control system comprising an external power supply, a boosterset disposed to draw electrical energy from the external power supply,two motors with the booster armature disposed to be connected betweenthem to buck or boost the supply to the motors, transfer switchesdisposed to connect junction points of the booster and the motorarmatures with terminals of the said power supply, a switch fordisconnecting the booster from the said supply after closure of thetransfer switches, and a control relay for controlling the operation ofsaid transfer and disconnection switches, said relay having an operatingcoil connected across a transfer switch when the transfer switch is openand across the disconnecting switch when it is open, the operating coilof said relay being connected between a contact of one switch and acontact of the other, a rectifying valve in series with said coil toprevent passage of current until the potential difference across thetransfer switch has reached zero, and a source of biasing voltage foroperating the relay when said potential difference is substantiallyzero.

'1. A motor control system comprising an eitternal power supply, abooster set disposed to draw electrical energy from the external powersupply, two motors with the booster armature disposed to be connectedbetween them to buck or boost the supply to the motors, transferswitches disposed to connect junction points of the booster and themotor armatures with terminals of the said power supply, a switch fordisconnecting the booster from the said supply after closure of thetransfer switches, and a control relay having an operating coilconnected across a transfer switch when the transfer switch is open andacross the disconnecting switch when it is open, said control relaybeing adapted to effect retransference of said connections upon arestoration of predetermined conditions.

8. A motor control system comprising an external power supply, a boosterset disposed to draw electrical energy from the external power supply,two motors with the booster armature disposed to be connected betwenthem to buck or boost the supply to the motors, transfer switchesdisposed to connect junction points of the booster and the motorarmatures with terminals of the said power supply, a switch for,

disconnecting the booster from the said supply after closure of thetransfer switches, a control relay having an operating coil connectedacross a transfer switch when the transfer switch is open and across thedisconnecting switch when I it is open, the operating coil of said relaybeing connected between a contact of one switch and a contact of theother, a. rectifying valve in series with said coil to prevent passageof current until the potential difference across the transfer switch hasreached zero, a source of biasing voltage for operating the relay whensaid potential difference is substantially zero, a polarizing coil onthe control relay, and switching means responsive to the operation ofthe relay to reverse the polarity of the polarizing coil whereby arestoration of conditions producing current in the operating coil afteroperation of the relay to effect transfer will move the relay back toeffect re-transfer.

9. A motor control system comprising an external power supply, a boosterset disposed to draw electrical energy from the external power supply,two motors with the booster armature disposed to be connected betweenthem to buck or boost the supply to the motors, transfer switchesdisposed to connect junction points of the booster and the motorarmatures with terminals of the said power supply, a switch fordisconnecting the booster from the said supply after closure of thetransfer switches, a control relay having an operating coil connectedacross a transfer switch when the transfer switch is open and across thedisconnecting switch when it is open, the operating coil of said relaybeing connected between a contact of one switch and a contact of theother, a'rectifying valve in series with said coil to prevent passage ofcurrent until the potential difference across the transfer switch hasreached zero, a source of biasing voltage for operating the relay whensaid potential difference is substantially zero, a polarizing coil onthe control relay, and switching means responsive to the operation ofthe relay to reverse the polarity of the polarizing coil whereby arestoration of conditions producing current in the operating coil afteroperation of the relay to effect transfer will move the relay back toeffect retransi'er, and means for causing the reversing switch for thepolarizing coil of the relay to operate with a time-lag.

10. A motor control system comprising a directcurrent traction motor, anexternal power supply, a booster set disposed to draw electrical energyfrom the external power supply and to buck or boost the supp to themotor to maintain substantially a predetermined current through thetraction motor armature, a master controller disposed to control closureof circuits 5 for accelerating the traction motor, and control means forautomatically transferring the load formed by the motor armature to thepower supply without further movement of the master controller when thecounter electro-motive force for 10 the traction motor is substantiallyequal to the said power supply voltage.

11. Electric motor and control equipment comprising, in combination, adirect-current motor, an external power supply, a booster set disposedll to draw electrical energy from the external power supply and to buckor boost the supp y to the motor to maintain substantially apredetermined current through the traction motor armature duringacceleration and regenerative braking of I the motor, a separatelyexcited field winding on the motor, means for energizing said winding asa continuous function of motor speed, means for transferring the loadformed by the motor armature from the said booster to the externalsupply, control means for said transfer means responsive to theelectrical condition of the said motor circuit, and a rectifying valvein series with an operating coil of the control means whereby the saidcontrol means will respond to a potential difference of only onepolarity.

12. Electric motor and control equipment comprising, in combination, adirect-current motor,

an external power supply, a booster set disposed to draw electricalenergy from the external power supply and to buck or boost the supply tothe motor to maintain substantially a predetermined current through thetraction motor armature during acceleration and regenerative braking ofthe motor, a separately excited field winding on the motor, an auxiliarydynamo-electric machine driven by the motor for energizing said windingas a continuous function of motor speed. means for transferring the loadformed by the motor armature from the said booster to the externalsupply, control means for said transfer means responsive to theelectrical condition of the said motor circuit, a rectifying valve inseries with an operating coilof the control meanswhereby the saidcontrol means will respond to a potential difference of only onepolarity, and a source of biasing voltage in series with the said coiland valve and tending to send current in the direction permitted by thevalve.

ERIC ALTON BINNEY.

HAROLD SINCLAIR POUND-CORNER.

HUGH BROUGBAM swarm.

